This invention relates to an azeotrope containing hydrogen fluoride (referred to hereinafter as "HF") and 1,1,1-trifluoro-3-chloro-2-propene (referred to hereinafter as "1233zd"), to methods for separating this azeotrope from mixtures of HF and 1233zd which are HF-rich or 1233zd-rich, and to methods for making use of the azeotrope and separation methods to improve processes for preparing 1233zd, a known intermediate for the preparation of 1,1,1,3,3-pentafluoropropane (referred to hereinafter as "245fa"), as taught, for example in U.S. Pat. No. 5,616,189. 245fa is known to have utility as a foam blowing agent and refrigerant.
A number of processes in the prior art make 245fa by first making the 1233zd intermediate. For example, 1233zd can be made by fluorination of 1,1,1,3,3-pentachloropropane ("240fa") or fluorination of 1,1,3,3-tetrachloro-2-propene (referred to hereinafter as "1230za"). The 1230za is of special interest as a starting material since it has been shown to fluorinate readily in the liquid phase without a catalyst, as taught in copending U.S. Pat. application Ser. No. 09/013,839, filed Jan. 27, 1998 (now U.S. Pat. No. 5,877,359). The 1233zd intermediate can then be fluorinated directly or through other intermediates to make 245fa. One of the problems associated with the 1233zd intermediate, however, is that it has the same boiling point (20.degree. C.) as HF, posing a problem of how to recover sufficient HF to make the process economical.
Heterogeneously catalyzed gas phase processes can also be used for fluorinating 240fa or 1230za to 1233zd, as disclosed, for example, in Application WO 97/24307 and copending U.S. Pat. application Ser. No. 08/980,746, filed Dec. 1, 1997, (now U.S. Pat. No. 5,811,603). A major problem associated with gas phase reactions, however, is that the precursor compounds have high boiling points (179.degree. C. for 240fa and 149.degree. C. for 1230za) and low thermal stability at elevated temperatures. Furthermore, their decomposition can be catalyzed in the liquid phase by acids such as HF, which is a reactor feed. It would thus be useful to develop a process which could be used to lower the volatility of the organic feed and thereby avoid its thermal decomposition.
In this application "distillation column" and "rectification column" are sometimes used interchangeably. Actually, however, a rectification column is a specific type of distillation column. In most distillation columns the material to be distilled is fed to the middle of the column; below the feed point is called the stripping section and above the feed point is called the rectification section. Reference is made herein to a rectification column when the material to be distilled is instead fed to the bottom of the "distillation column."